how wings work? Smoke streamlines around an airfoil

Department of Engineering, University of Cambridge, multimedia video from Physics Education, 2003, by Holger Babinsky.

Category:

Science & Technology

Tags:

• airflow
• airfoil
• smoke
• streamline
• visualization
• bernoulli

[completeaerogeek]

@g1geo1g -No worries. Yes that right. The shape of a wing can vary. All airliners use supercritical wings which are flatter on top and curved on the bottom with a reflex curve at the underside trailing edge. This increases the critical Mach number and reduces the size of the shock wave and the associated drag allowing for a higher MMO. Helicopters and aerobatic aircraft use symmetrical aerofoils which of course blows up the 'Venturi explanation and the equal transit time one as well.

[g1geo1g]

@completeaerogeek, thanks as well for the sail explanation. I would just like to clarify that the sail 'luffs' when parallel to the apparent wind ie when an attempt is made to use it similarly to a solid airfoil. It is only through the turning of the air and momentum exchange that it becomes a curved surface. Also the stalled condition for a wing 'is' the parachute condition for a sail.

[g1geo1g]

@completeaerogeek, thanks as well for the sail explanation. I would just like to clarify that the sail 'luffs' when parallel to the apparent wind ie when an attempt is made to use it similarly to a solid airfoil. It is only through the turning of the air and momentum exchange that it becomes a curved surface.

[g1geo1g]

@completeaerogeek, thanks, that's a much more satisfying explanation than 'the wing turns the flow'. Yes the pressure before the leading edge is of particular interest, becoming a dynamic extension of the wing's leading edge. The shearing information and the collapse behind the wing are both functions of the air (as you said) leading to differences in response as the wing approaches sound speed. Hence the need for different profiles.

[completeaerogeek]

@g1geo1g -Also remember that the air is not moving the wing is. The passage of the wing displaces air and creates a void which begins to collapse as the highest thickness/chord passes through, This collapse is caused by the normal air pressure acting on the shrinking void this shrinking and air's natural viscosity which causes it to follow a curved surface (Coanda)  lowers the pressure below static You can see this as the streamlines spread out slightly. NASA knows it's stuff.

[completeaerogeek]

@g1geo1g 0 - In a sail boat the turning flow produces lift force that causes the boat to heel in close hauled conditions. This is opposed by the keel and rudder not unlike side slip/crabbing in an aircraft, When the wind is anywhere from 30 deg to 90 deg off the bow the wing is producing turning flow. On a broad reach the sail produces lift/turning flow with reversed airflow When running the sail acts more like a parachute thus is has modes aircraft do not. A sail cannot work if stalled-it luffs

[completeaerogeek]

@g1geo1g - If you look at the streamlines you can see that the bow wave of the wing is affecting the streams before the air reaches the wing.then air has to divide as the wing pushes through. If you look at pressure distribution the over an aerofoil there is in fact a high pressure at the stagnation point ( and slightly above it) so you are partly correct.. As the air turns the corner is is pulled into the lower pressure area created by the forward movement of the wing= rearward downward vector

[g1geo1g]

Also 'lift' can be used out of context.. Any solid object produces 'lift' in an airstream. It is a component of the net force at right angles to the flow. A sailboat, for instance, produces 'lift'. It also produces 'sailboat drive' and 'heel' both 'relevant' to the boats motion. 'lift' only coincides with 'sailboat drive' when the wind is across the beam. A sail still works in full drag when the 'lift' tends to zero.

[g1geo1g]

@completeaerogeek, thanks for the input. Mmmmm. Not convinced. If the wing pushes the air up to create the low pressure then that pushes the wing down (Newton' third). Also air cannot 'turn a corner' unless acted upon by an external force (Newton's first). Are you comfortable about the truths of Newton's laws wrt non relativistic physics?

[completeaerogeek]

Part of the key to what the video shows is that the air above is not dramatically affected- (watch the free stream reference lines) rather the pressure wave created by the lower surface has a huge influence on the pressure differential as it pushes the air forwards and down-much like a bow wave. Pushing the air out of the way creates a semi void (LP) on the upper surface (hence the need for an AOA for lift to be created) the air turns the corner and follows the upper surface = downward vector..